Background #
I’m not exactly sure which cars have this, or are supposed to have this. The later MGBs did not use the oil cooler and use a bypass connection between the block and the oil filter adapter. On some really late cars, like the MGB LE, I have seen this is a hard line. On my 1977 MGB, I have a flexible bypass hose. So, whether this will impact you can come down to (a) you don’t have an oil cooler installed and (b) the bypass hose is a flexible one, versus a hard line.
I had replaced this hose on my 77B at some point in the past. But I don’t exactly remember when – probably 10+ years ago. The hose has a date of production on it from 2007 (09/07) so it was for sure in the 10 year range. If this hose fails it will cause catastrophic engine failure. It was time to do a preventative replacement. Upon closer inspection, this was definitely needed. It appears the snorkel from the air pump filter cover had been resting on and vibrating against the hose. This wearing away of the outer rubber cover and starting to show the inner part of the hose materials.
Step by Step #
Here is the process I followed to do my Oil Cooler Bypass Hose replacement.
Step 1 Making Room #
In order to remove this hose you will need to make some working space.The car was due for an oil change anyway, this was the perfect time. The oil was drained and I removed the oil filter. I then prepared to remove the distributor. To avoid having to adjust the timing afterwards, I marked the position of the distributor against its clamp with a Sharpie. A small mark on the clamp and the lip of the distributor does the trick.
You can then loosen the distributor clamp with a 7/16ths wrench (spanner). Gently remove the distributor by moving it side to side (front to back of the car) while pulling towards you. You may need to loosen more and possibly spread the clamp to increase the gap at the top. Use a big flat head screw driver. Once the distributor is out, put it to one side. Don’t crank or otherwise have the engine turn over/move.
Step 2 Removing the Old Hose #
Now you can remove the small oil pressure gauge hose connection from the back of the block. This is just next to where the oil bypass hose connects. For me this was also a 7/16ths wrench but with replacement hoses yours may differ. Now you will have full access to the connector of the oil bypass hose on the back of the block. Not sure exactly what size this is – approx. 15/16ths. Get that rear one loose. Then you can break loose the front connector on the oil filter adapter right behind the alternator. With both ends of the hose loose complete the removal of the hose. Given this is likely to be full of oil so take precautions. For example don’t be holding the respective ends of the hose while one of your arms is around the bonnet prop!
Step 3 Installing New Hose #
Install the new hose. Note that the 90 degree connection end attaches to the oil filter assembly and the offset end attaches to the block. Get these connections really tight. Particularly the rear engine block connection, because you don’t want a leak and to have to remove everything again. Take it a little easier with the oil filter adapter connection. This needs to be tight, of course, you’ll have oil at 75/80 lbs pressure going through it. But you can get to it without removing stuff. I decided to offset the angle of the hose a bit more this time. So it is now a little closer to the coil and if the air pump filter snorkel moves around, it won’t hit the oil bypass hose anymore. I also tightened the nut on the air pump filter case to try and stop it moving so easily.
Step 4 Wrapping Things Up #
Then you can re-attach the oil pressure gauge hose and reinstall the distributor. You may need to fiddle around with the rotor on the distributor to get it to fit in correctly (mating with the drive dog). Take the cap off will allow this.
The distributor must be flush against the holding bracket. If not pull it out and try again and possibly open the clamp a little more with a flat head screw driver. Once the distributor is in correctly, align the marks you made and clamp it down in place. Don’t over tighten the clamp – it just needs to hold the distributor in the set location. If you crank down on the clamp you’ll crack the distributor casing. Less is more in this case! Make sure to reconnect your vacuum advance and put the cap back on the distributor and plug wires in the correct 1,3,4,2 firing order.
If you removed the oil filter, as I did but it’s not required, install a new oil filter. You’re now done. Get oil pressure up by turning the car over on the starter without the engine firing. I do this by removing my Pertronix ignition wires. Make sure you get oil pressure and do a first check for leaks.
If all is well connect things back up and let the engine fire up and again check for leaks.Hopefully you have none and now you can relax knowing you have a new oil bypass hose in place which will hopefully ensure you don’t have a sudden leak and have 4-5 quarts of oil exit your engine in a matter of seconds! A good preventative bit of maintenance. Particularly if you have no idea how old the hose is. As a last note my new hose didn’t have a date of manufacture on the black hose piece as before, but there was a tiny sticker on one of the fittings that provided this information.
Other Materials #
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